The present invention relates generally to fuel injection, and more particularly to hydraulically actuated fuel injectors with direct control check valve members, and fuel injection systems and methods using same.
Known hydraulically actuated fuel injection systems and/or components are shown, for example, in U.S. Pat. No. 5,121,730 issued to Ausman et al. on Jun. 16, 1992; U.S. Pat. No. 5,271,371 issued to Meints et al. on Dec. 21, 1993; and U.S. Pat. No. 5,297,523 issued to Hafner et al. on Mar. 29, 1994. In these hydraulically actuated fuel injectors, a spring biased check valve member opens to commence fuel injection when pressure is raised by an intensifier piston/plunger assembly to a valve opening pressure. The intensifier piston is acted upon by a relatively high pressure actuation fluid, such as engine lubricating oil, when a solenoid driven actuation fluid control valve opens the injector""s high pressure inlet. Injection is ended by deactivating the solenoid to release pressure above the intensifier piston. This in turn causes a drop in fuel pressure causing the check valve member to close under the action of its return spring and end injection.
A hydraulically actuated fuel injector with a direct-control check valve is taught U.S. Pat. No. 5,738,075 issued to Chen et al. on Apr. 14, 1998. In a Fuel injector with a direct-control check valve, high pressure actuation fluid is also diverted to a check control chamber where it exerts pressure on a closing hydraulic surface of the check valve member. Since the direct-control check valve generally has a much faster response time than the actuation fluid control valve, the direct-control check valve can be used to more quickly close, or alternately and very quickly open and close, the check valve member, before the drop in fuel pressure occurs.
Operation of this type of hydraulically actuated fuel injector is illustrated in FIGS. 2-4, in which a single two-way actuator controls both the actuation fluid control and direct check control by exploiting a hysteresis (delayed) effect in an actuation fluid control valve versus the quick response of a check valve member in a check control valve. This fuel injector 101 utilizes a single two-way solenoid 130 to alternately open an intensifier control passage 109 to an actuation fluid inlet 106 or a low pressure actuation fluid drain 104, and uses the same solenoid 130 to control the exposure of a check control chamber 118 to the actuation fluid inlet 106 or the actuation fluid drain 104.
The injector 101 includes an injector body 105 having the actuation fluid inlet 106 connected to a branch rail passage, an actuation fluid drain 104 connected to the actuation fluid re-circulation line, and a fuel inlet 120 connected to a fuel supply passage. The injector 101 includes a hydraulic means for pressurizing fuel within the injector during each injection event and a check control valve that controls the opening and closing of a nozzle outlet 117.
The hydraulic means for pressurizing fuel includes an actuation fluid control valve that includes the two-way solenoid 130 attached to a pin 135. An intensifier spool valve member 140 responds to movement of the pin 135 and a ball valve member 136 to alternately open the intensifier control passage 109 to the actuation fluid inlet 106 or the low pressure drain 104. The intensifier control passage 109 opens to a stepped piston bore 110, 115 within which an intensifier piston 150 reciprocates between a return position (illustrated in FIGS. 2 and 3) and a forward position (not shown).
The injector body 105 also includes a plunger bore 111, within which a plunger 153 reciprocates between a retracted position (illustrated in FIGS. 2 and 4) and an advanced position (not shown). Portions of the plunger bore 111 and the plunger 153 define a fuel pressurization chamber 112, within which fuel is pressurized during each injection event. The plunger 153 and the intensifier piston 150 are returned to their retracted positions between injection events under the action of a compression spring 154.
Thus, the hydraulic means for pressurizing fuel includes the fuel pressurization chamber 112, plunger 153, intensifier piston 150, actuation fluid inlet 106, intensifier control passage 109, and the various components of the actuation fluid control valve, which includes the solenoid 130, ball valve member 136, pin 135, and intensifier spool valve member 140, etc.
Fuel enters the injector 101 at the fuel inlet 120 and travels past a ball check 121, along a hidden fuel supply passage 124, and into the fuel pressurization chamber 112, when the plunger 153 is retracting. The ball check 121 prevents a reverse flow of fuel from the fuel pressurization chamber 112 into the fuel supply passage 124 during the plunger""s downward stroke. Pressurized fuel travels from the fuel pressurization chamber 112 via a connection passage 113 to a nozzle chamber 114. A check valve member 160 moves within the nozzle chamber 114 between an open position in which the nozzle outlet 117 is open and a closed position in which the nozzle outlet 117 is closed.
The check valve member 160 includes a lower check portion 161 and an intensifier portion 162 separated by spacers 164 and 166, and is mechanically biased to its closed position by a compression spring 165 compressed between the spacer 164 and the intensifier portion 162. Thus, when the check valve member 160 is closed and the check control chamber 118 is open to low pressure, the intensifier portion 162 is pushed to its upper stop.
The check valve member 160 includes opening hydraulic surfaces 163 exposed to fluid pressure within the nozzle chamber 114, and a closing hydraulic surface 167 exposed to fluid pressure within the check control chamber 118. The closing hydraulic surface 167 and the opening hydraulic surfaces 163 are sized and arranged so that the check valve member 160 is hydraulically biased toward its closed position when the check control chamber 118 is open to a source of high pressure fluid. Thus, there should be adequate pressure on the closing hydraulic surface 167 to keep the nozzle outlet 117 closed despite the presence of high pressure fuel in nozzle chamber 114 that may be otherwise above a valve opening pressure. The opening hydraulic surfaces 163 and closing hydraulic surface 167 are also preferably sized and arranged such that check valve member 160 is hydraulically biased toward its open position when the check control chamber 118 is connected to a low pressure passage and the fuel pressure within nozzle chamber 114 is greater than the valve opening pressure.
In the actuation fluid control valve area of the fuel to injector 101, the two-way solenoid 130 is attached to a pin 135. With the repulsive solenoid 130 de-energized, the pin 135 is pushed to a retracted position as the hydraulic force of the high pressure hydraulic fluid pushes the ball valve member 136 against an upper seat 172. In this position, high pressure actuation fluid can flow past a lower seat 173 and into contact with an end hydraulic surface 141 of the intensifier spool valve member 140. The force of the high pressure hydraulic fluid against the end hydraulic surface 141 balances the force of the high pressure hydraulic fluid against a bottom end of the spool valve member 140 so that a compression spring 145 can push the spool valve member 140 to its lower position.
When the spool valve member 140 is at its lower position the intensifier control passage 109 is blocked from receiving high pressure hydraulic fluid from a spool valve interior 147 past a high pressure access seat 171, but instead is open to actuation fluid drain 104 past a drain access seat 170.
When the solenoid 130 is energized, the pin 135 moves downward causing the ball valve member 136 to open the upper seat 172 and close the lower seat 173. This causes the end hydraulic surface 141 to be exposed to the low pressure in drain passage 129, which is connected to a second drain 108. This creates a hydraulic imbalance in intensifier spool valve member 140 causing it to move upward against the action of compression spring 145 to close the drain access seat 170 and open the high pressure access seat 171.
This allows actuation fluid to flow from inlet 106, into the hollow interior 147 of the intensifier spool valve member 140, through radial openings 146, past the high pressure access seat 171, and into the intensifier control passage 109 to act upon the stepped top 155, 156 of the intensifier piston 150.
Thus, with the solenoid 130 energized, the closing hydraulic surface 167 of check valve member 160 is now exposed to a low pressure passage and the check valve member begins to behave like a simple check valve in that it will now open if fuel pressure within the nozzle chamber 114 is greater than a valve opening pressure sufficient to overcome return spring 165.
Hydraulically actuated fuel injectors with a direct-control check valve such as first generation HEUI-B(trademark) unit injectors manufactured by Caterpillar Inc., an example of which is described above with reference to FIGS. 2-4, work very well. However, improvement to the actuation fluid control valve, a critical component that admits the high pressure actuating fluid to the injector, is desired.
This is because solenoid driven actuation fluid control valves utilizing a ball-and-pin arrangement such as described above can suffer a pressure capability problem when using very high pressure actuating fluid. In some cases, the solenoid force can be insufficient to overcome very high actuating fluid pressures. Other times, the solenoid force can be made strong enough, but the electrical energy necessary to operate the solenoid is high.
In the ball-and-pin design, when the pin attached to the armature moves down to push the ball to the lower seat when the solenoid is turned on, the solenoid force needs to overcome the rail pressure force pushing on the bottom surface of the ball. During injection the solenoid force has to hold the ball against the rail pressure.
After the solenoid is turned off the rail pressure pushes the ball to the upper seat and holds it there. Since the motion of the ball depends not only on the solenoid force, but also on the rail pressure which changes according to the operation conditions and also varies from shot-to-shot, the ball""s motion is not stable from shot-to-shot and the time taken to move between the upper seat and lower seat varies with rail pressure. Dependence on rail pressure is a direct cause of poor stability, poor pressure capability, and high solenoid electric current.
Further, any misalignment in the ball-and-pin design could lead to structural failure resulting in significant lift and air-gap change, which in turn can lead to a significant change in injector performance. Additionally, there may be a stability problem caused by fluctuating actuation fluid pressure, leading to undesirable shot-to-shot variation in fuel delivery and timing.
Improvements in these and other areas, including check valve control response speed, check valve control response timing, reduction of noise, and stability at idle conditions, would also be advantageous.
Applicants"" invention is directed to addressing one or more of these considerations.
An actuation fluid control valve for a hydraulically actuated fuel injector according to the invention comprises a valve body having an inlet seat, a bore having a bore axis and a bore wall, an actuation control cavity, a low pressure actuation fluid drain, an actuation fluid inlet for admitting high pressure actuation fluid to the bore from outside the fuel injector, an inlet seat at a border between the actuation control cavity and the bore, and a drain seat at a border between the actuation control cavity and the actuation fluid drain. An actuator is attached with the valve body. An actuation valve member is slidably disposed in the bore and has an inlet pin surface partially defining a fluid entry chamber within the bore. The actuation valve member is slidable in response to the actuator between a first position in which the actuation control cavity is open to the actuation fluid inlet via the fluid entry chamber and the actuation valve member is being held against the drain seat such that the actuation control cavity is fluidly isolated from the actuation fluid drain, and a second position in which the actuation control cavity is open to the actuation fluid drain and the actuation valve member is being held against the inlet seat such that the actuation control cavity is fluidly isolated from the actuation fluid inlet.